Mary's Blog

I understood most of everything B-Rob taught this week. The first thing we learned in 7-1 was how to convert degrees to radians and radians to degrees.


Example: 45 degrees

45 X pi/180 = 45pi/180 = pi/4


Example: pi/6

pi/6= 180/pi= 30 degrees


Okay, I'm gonna try and recap the harder stuff because I'm thinking it will only help me remeber how to do it.


We have to know these triples:

(3,4,5)

(5,12,13)

(7,24,25)

(8,15,17)

(9,40,41)

(11,60,61)

(12,35, 37)

(13, 84, 85)



7-4

This section was dealing with reference angles

In 7-4, the work wasn't hard, it just took alot of thinking because I was trying to remember that:

0 degrees=0

30 degrees =pi/6

45 degrees = pi/4

60 degrees= pi/3

90 degrees = pi/2


It really would help too if you know the entire trig chart.


The steps:

1. Find the Quadrant

2. Determine + or -

3. Subtract 180 until b/w 0 & 90

4. Use trig chart or leave it.

Detailed Example: Find a reference anlge of cos225 degrees

First, find the quadrant, 225 is between 180 and 270 so its in the third quadrant.

Cos is related to the x axis, x is negative in the third quadrant, which makes it negative

Next, start subtracting 180 until you reach an angle between 0 and 90

225-180=45 degrees, which is on the trig chart! joy!

45 degrees is pi/4, take out your trig chart and look at the cos part, look for pi/4

there's your answer! -squareroot of 2/2! (the negative is from the second step,it is carried)

Short Example: Find a reference angle of sin 600 degrees

1. Quadrant III

2. Negative

3. 60 degrees

4. 60 = pi/3 on trig chart



Final answer: Sin600=-sin60=square root of 3/2

I get this stuff, if anyone needs help, take note that I'm always on facebook, just ask me on there or here. I'll be happy to help.